Research

Superconductor semiconductor quantum optoelectronic devices

Various applications in the rapidly growing field of quantum information science require reliable and efficient quantum light sources. We observed superconducting proximity in semiconductor light-emitting diodes. These hybrid structures were proposed by us as an efficient approach for generation of entangled photons, based on Cooper-pair luminescence in semiconductors. We study a new effect of enhanced light amplification in electrically-driven semiconductor-superconductor structures, including Cooper-pair based two-photon gain. Moreover, we investigate a compact and highly-efficient scheme for a complete Bell-state analysis using two-photon absorption in a superconducting proximity region of a semiconductor avalanche photodiode. This Cooper-pair based two-photon absorption results in a strong detection preference of a specified entangled state.

High-temperature superconductor semiconductor optoelectronic devices

The interaction of light with semiconductor-superconductor structures has recently emerged as a new interdisciplinary field of superconducting optoelectronics with demonstrations of light emission from hybrid light-emitting diodes enhanced by the superconducting state, and various proposals for novel lasers and quantum light sources. These hybrid devices have also proven useful in nonlinear electronics and infrared detection taking advantage of the superconducting gap in the tunneling spectrum. However, all previously studied semiconductor-superconductor devices were based on conventional low-Tc superconductors, requiring extreme cooling. We demonstrated a hybrid high-Tc-superconductor-semiconductor tunnel diode constructed from Bi₂Sr₂CaCu₂O_8+δ combined with bulk GaAs or with a GaAs/AlGaAs quantum well, which shows excess voltage and nonlinearity - in good agreement with theoretical predictions for a d-wave superconductor-normal material junction.

We also show high-Tc Cooper-pair injection into semiconductors, and demonstrated ultrafast high-Tc superconducting photodetectors, paving the way for more practical applications.

High-temperature topological superconductor devices

Producing new effects through the combination of different materials has a long history in science and technology. One of the most intriguing recent ideas is the emergence of Majorana fermions when a topological insulator is placed in proximity with a superconductor. Towards this goal, we produced high-temperature superconductivity in the topological insulator Bi₂Se₃ via the proximity to Bi₂Sr₂CaCu₂O_8+δ. This was achieved through a new mechanical bonding technique enabling the fabrication of high-quality junctions between novel materials, unobtainable by conventional approaches. The results presented here open new directions for fundamental studies in condensed matter physics and enable a wide range of applications in spintronics and quantum computing.

Exciton–polariton ultrafast condensate dynamics, devices and circuits

Strong coupling has been studied in atomic physics since the first demonstrations of vacuum Rabi splitting which manifests the new dressed eigenstates of the system. In semiconductors, these dressed states correspond to new quasi-particles when quantum well excitons are strongly coupled to a microcavity mode. Exciton-polaritons which emerge from this strong coupling have a unique combination of extremely low effective mass and strong polariton-polariton interactions which enable observations of a wide range of physical phenomena including strong parametric scattering, and high-temperature Bose-Einstein condensation (BEC). Optical manipulation of exciton-polariton BEC was recently achieved by potentials created by repulsive interaction between excitons. The switching speed of these potentials based on carrier generation, however, is limited by the carrier dynamics, preventing fast manipulation and characterization of the condensate. Our demonstration of the dynamic Stark shift of exciton-polaritons can provide a fast-switching and density-independent technique of manipulating and reconstructing the state of the condensate using quantum tomography. This approach may also enable the interaction of quantum vortices of the condensate with orbital angular momentum of light for storing and processing quantum information.

We also reported the first experimental observation of two-photon pumped polariton condensation, demonstrated by angle-resolved photoluminescence in a GaAs-based microcavity. Our results pave the way towards polariton-based THz lasing and coherent control of collective quantum states with individual qubits

Ultrafast spin-based devices in topological insulators

Topological insulators (TIs) are becoming a topic of great interest in both fundamental physics and in technological applications, due to their remarkable properties, with an insulating bulk and topologically protected metallic surface states. These surface states exhibit massless Dirac dispersion, as well as locking of spin orientation to the momentum vector, resulting in dissipationless spin currents enabling spintronic devices. We demonstrate efficient linear-optical access to TI Bi2Se3 ultrafast spin dynamics by broadband time-resolved transient reflectivity measurements. This enables a practical technique to access spin-current behavior in TI based devices. We exploit the interplay between co- and anti-circular polarizations of the pump and the probe photons at oblique incidence – to distinguish between bulk and surface state responses in optically-excited transitions between two Dirac cones in Bi2Se3 , separated by approximately 1.5 eV

Two-photon processes in semiconductors

Efficient processes of two-photon absorption and two-photon emission in semiconductors can provide foundations for novel building blocks for quantum communications, integrated nonlinear optics and ultrafast optics. We demonstrated experimentally the first observation of two-photon emission in semiconductors - a process, in which electron transition between energy levels occurs by the emission of a photon pair. Spontaneous and singly-stimulated two-photon emission in bulk GaAs and in electrically driven quantum wells were observed at room temperature, and a divergence-free theoretical model was developed. We proposed this phenomenon as an electrically-driven room-temperature source of entangled photons, much more efficient than down-conversion schemes. We also proposed two-photon absorption for infrared photon detection in wide-gap semiconductors and for interferometric characterization of energy qubits. First observations of electrically-induced two-photon transparency and two-photon gain in semiconductor waveguides are demonstrated experimentally, and employed for pulse compression.

Semiconductor integrated nonlinear optics

Semiconductors are promising nonlinear materials due to their high susceptibilities and compatibility with the existing photonics technology. We introduce a new concept of standing-wave microcavity nonlinear optics for materials which cannot be phase-matched by conventional means. High quality factor cavities are also shown to serve as storage for the produced photons and generate time-separation between exiting photons for photon-number-resolved detection. We design and fabricate integrated semiconductor microcavities for self-phasematched second harmonic generation, employing a newly developed technique for high-aspect-ratio focused ion beam semiconductor nanopatterning.

Ultrafast multi-photon detection

We demonstrate experimentally ultrafast three-photon counting by three-photon absorption in a GaAsP photomultiplier, which may serve as a tool for ultrafast quantum state characterization as well as for ultrasensitive third-order temporal measurements. We introduced and realized a compact semiconductor-based scheme for a femtosecond-scale partial fourth-order coherence g⁽⁴⁾ measurements based on a start-stop photon-counting HBT interferometry of SHG, allowing compact characterization devices for photon-pair statistics.

Time-energy quantum information

In contrast to the internal polarization degree of freedom of a photon limited only to two dimensions, external degrees of freedom related to space and time are described by infinite-dimensional Hilbert spaces. We study a multidimensional quantum information approach based on photon temporal phase modulation, where the Hilbert space is spanned by an infinite set of orthonormal temporal phase profiles. Temporal phase modulation may enable multidimensional quantum information applications over the existing fiber optical infrastructure, as well as an avenue for probing high-dimensional entanglement approaching the continuous limit. We proposed a compact source of energy-entangled photons based on the efficient second-order process of two-photon spontaneous emission from electrically pumped semiconductor quantum wells in a photonic microcavity. Photon energy-qubits and schemes for photon energy entanglement characterization are investigated by a two-photon absorption interferometer based on electron transition path interference.

Weak measurement metrology

Quantum photonic sources can be employed for novel metrology schemes based on weak measurements, which allow probing of phenomena previously deemed inaccessible. Unlike the uncertainty relation, another relation postulated by Heisenberg setting the limit on measurement precision resulting in disturbance, was proven to be inaccurate, in contrast to widely-accepted limitations of high-precision metrology. We present an experimental realization of Heisenberg’s precision limit violation for photon spin, based on weak value measurements employing polarization-entangled photon pairs from downconversion. We show theoretically that weak measurements can be used to enhance optical nonlinearities at the single photon level, offering an improvement in signal-to-noise ratio in the presence of long-correlation technical noise.